Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A liquid crystal display (LCD) including a LCD panel, a first polarizer
and a second polarizer respectively disposed at two sides of the LCD, a
first a-plate and a second a-plate disposed between the polarizers and
LCD panel, a biaxial compensation plate and a c-plate is provided. The
biaxial compensation plate is disposed between one of the polarizers and
one of the a-plates. The main axis refractive indexes nx, ny
and nz of the biaxial compensation plate satisfy the formula of
Nz=(nx-nz)/(nx-ny), wherein nx>ny and
-0.5<Nz<1. The first c-plate is disposed between one of the
a-plates and LCD panel. The LCD of the present invention is capable of
widening viewing angles and enhancing display quality.

Claims:

1. A liquid crystal display, comprising: a liquid crystal display panel
having a vertical alignment liquid crystal layer; a first polarizer and a
second polarizer respectively disposed at two sides of the liquid crystal
display panel; a first a-plate and a second a-plate, wherein the first
a-plate is disposed between the liquid crystal display panel and the
first polarizer, and the second a-plate is disposed between the liquid
crystal display panel and the second polarizer; a biaxial retardation
plate disposed between the first a-plate and the first polarizer or
disposed between the second a-plate and the second polarizer, wherein the
biaxial retardation plate has a plurality of main axis refractive indexes
nx, ny and nz, and the main axis refractive indexes
nx, ny and nz satisfy the formula:
Nz=(nx-nz)/(nx-ny) wherein nx>ny, and
-0.5<Nz<1; and a first c-plate disposed between the liquid crystal
display panel and the first a-plate or disposed between the liquid
crystal display panel and the second a-plate.

2. The liquid crystal display of claim 1, wherein the first c-plate
provides a first phase retardation in vertical direction, and the first
phase retardation in vertical direction is substantially 215 nm.+-.100
nm.

3. The liquid crystal display of claim 1, further comprising a second
c-plate, wherein the first c-plate and the second c-plate are
respectively adjacent to two sides of the liquid crystal display panel.

4. The liquid crystal display of claim 3, wherein the first c-plate
provides a first phase retardation in vertical direction, the second
c-plate provides a second phase retardation in vertical direction, each
of the first phase retardation in vertical direction and the second phase
retardation in vertical direction is substantially 107.5 nm.+-.50 nm.

5. The liquid crystal display of claim 1, wherein the first a-plate
provides a first phase retardation in planar direction, the second
a-plate provides a second phase retardation in planar direction, each of
the first phase retardation in planar direction and the second phase
retardation in planar direction is substantially 140 nm.+-.50 nm.

6. The liquid crystal display of claim 1, wherein each of the first
a-plate and the second a-plate is a uniaxial optical compensation film.

9. The liquid crystal display of claim 8, wherein the phase retardation
in planar direction Rin provided by the biaxial compensation plate
satisfies the relationship of =(nx-ny)×d, wherein d is a
thickness of the biaxial compensation plate, and the phase retardation in
planar direction Rin is substantially 170 nm.+-.100 nm.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the priority benefit of Taiwan application
serial no. 98133828, filed on Oct. 6, 2009. The entirety of the
above-mentioned patent application is hereby incorporated by reference
herein and made a part of this specification.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a display apparatus, and more
particularly, to a liquid crystal display (LCD) having a vertical
alignment liquid crystal layer.

[0004] 2. Description of Related Art

[0005] Since the liquid crystal display is limited by its principle of
light emission, there remain some problems that urgently need mitigating.
For instance, the range of the viewing angle in the liquid crystal
display is too narrow. When a user views the liquid crystal display using
a too large viewing angle, the display quality, such as contrast ratio,
color saturation and luminance, is then lowered and is not as good as
during normal viewing.

[0007] Referring to FIG. 1A, the TFT array substrate 110 is disposed on
the first polarizer 130, and the color filter substrate 120 is disposed
over the TFT array substrate 110. The second polarizer 140 is disposed on
the color filter substrate 120, and the vertical alignment liquid crystal
layer 150 is disposed between the TFT array substrate 110 and the color
filter substrate 120. The liquid crystal molecules in the vertical
alignment liquid crystal layer 150 are rotated to different degrees
according to the voltage difference between the TFT array substrate 110
and the color filter substrate 120, so that the vertical alignment liquid
crystal display 100 displays images.

[0008] In order to enhance the display quality of the vertical alignment
liquid crystal display, some optical films are added to further increase
the viewing angle of the liquid crystal display.

[0009] FIG. 1B is a schematic view showing the viewing angle-contrast of a
conventional vertical alignment liquid crystal display. Referring to FIG.
1B, the viewing angles in the base directions, such as top direction,
bottom direction, left and right directions, of the vertical alignment
liquid crystal display can be enhanced through the addition of optical
films. However, as shown in FIG. 1B, since the viewing angle in the
diagonal direction of the display surface still remains unsatisfactory,
the conventional vertical alignment liquid crystal display still leaves
much room for improvement. Therefore, how to entirely widen the viewing
angles in any direction of the vertical alignment liquid crystal display
to enhance the display quality thereof has become a major concern of the
liquid crystal display.

SUMMARY OF THE INVENTION

[0010] The present invention provides a liquid crystal display to entirely
enhance the viewing angle and the display quality thereof by using a
biaxial compensation plate.

[0011] The present invention provides a liquid crystal display includes a
liquid crystal display panel, a first polarizer, a second polarizer, a
first a-plate, a second a-plate, a biaxial compensation plate and a
c-plate. The LCD panel has a vertical alignment liquid crystal layer. The
first polarizer and the second polarizer are respectively disposed on two
sides of the LCD panel. The first a-plate is disposed between the LCD
panel and the first polarizer, and the second a-plate is disposed between
the LCD panel and second polarizer. The biaxial compensation plate is
disposed between the first a-plate and the first polarizer or disposed
between the second a-plate and the second polarizer, wherein the biaxial
compensation plate has a plurality of main axis refractive indexes
nx, ny and nz, and the main axis refractive indexes
nx, ny and nZ satisfy the formula of
Nz=(nx-nz)/(nx-ny), wherein nx>ny, and
-0.5<Nz<1. The first c-plate is disposed between the LCD panel and
the first a-plate or disposed between the LCD panel and the second
a-plate.

[0012] In one embodiment of the present invention, the above first c-plate
provides a first phase retardation in vertical direction, and the first
phase retardation in vertical direction Rth is substantially 215
nanometers (nm)±100 nm, for example.

[0013] The liquid crystal display of the preset invention has a biaxial
compensation plate satisfying a certain condition, such that the phase of
incident light after passing through the LCD panel can be adjusted
accordingly, and thus color shift phenomenon can be avoided. Accordingly,
the liquid crystal display of the present invention can widen the viewing
angle and enhance the display quality thereof.

[0014] In order to make the aforementioned and other objects, features and
advantages of the present invention more comprehensible, several
embodiments accompanied with figures are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and constitute a
part of this specification. The drawings illustrate embodiments of the
invention and, together with the description, serve to explain the
principles of the invention.

[0024] FIG. 6A and FIG. 6B illustrate a schematic view showing an actual
measuring chromaticity coordinates in different viewing angles of a
conventional LCD and one embodiment of the present invention LCD.

DESCRIPTION OF EMBODIMENTS

[0025] The LCDs of the present invention compensate the optical
performance of the light passing through the vertical alignment liquid
crystal layer by utilizing a biaxial compensation plate satisfying a
certain condition. The light passes through the biaxial compensation
plate satisfying a certain condition between the main axis refractive
indexes so as to obtain an optical performance of widening viewing angle.

First Embodiment

[0026] FIG. 2A illustrates a schematic view of a liquid crystal display
according to the first embodiment of the present invention. Referring to
FIG. 2A, the LCD 200 of the present embodiment includes a LCD panel 210,
a first polarizer 220, a second polarizer 230, a first a-plate 240, a
second a-plate 250, a biaxial compensation plate 260 and a c-plate 270.
The LCD panel 210 is mainly composed of a TFT array substrate 212, a
color filter substrate 214, and a vertical alignment liquid crystal layer
216 sandwiched between said two substrates 212 and 214. Due to the
intrinsic optical anisotropy of the liquid crystal molecules in the
vertical alignment liquid crystal layer, the whole display performance of
the LCD may be affected. This invention utilizes the biaxial compensation
plate 260 incorporated with the first a-plate 240, the second a-plate 250
and the first c-plate 270 to compensate the phenomena of viewing angle
limit, the color shift, or the light leakage due to the optical
anisotropy of the liquid crystal molecules in the vertical alignment
liquid crystal layer 216, so as to obtain effects of widening the viewing
angle, improving color shift phenomenon, and reducing light leakage
phenomenon. In the present embodiment, the phase retardation of the
vertical alignment liquid crystal layer 216 is substantially in a range
340 nm±100 nm.

[0027] More specifically, as shown in FIG. 2A, the first polarizer 220 and
the second polarizer 230 are respectively disposed at two sides of the
LCD panel 210. The first polarizer 220 and the second polarizer 230 have
a polarizing axis, respectively. When a light passes through the first
polarizer 220 or the second polarizer 230, the polarizing direction of
the light is rotated along the polarizing axis and renders the light as a
polarized light. The first a-plate 240 is disposed between the LCD panel
210 and the first polarizer 220, and the second a-plate 250 is disposed
between the LCD panel 210 and the second polarizer 230. In this
embodiment, the first a-plate 240, the biaxial compensation plate 260 and
the first c-plate 270 are disposed between the LCD panel 210 and the
first polarizer 220. The linear polarizing light passing through the
first polarizer 220 sequentially passes through the biaxial compensation
plate 260, the first a-plate 240, and the first c-plate 270 to perform
phase retardation, and then enters into LCD 210. The second a-plate 250
is disposed between the LCD panel 210 and the second polarizer 230, such
that the light emitted from the LCD panel 210 passes through the second
a-plate 250 to further performing phase compensation, and then is emitted
from the second polarizer 230.

[0028] It should be noted that the first a-plate 240 and the second
a-plate 250 are uniaxial optical compensation film, for example. For
instance, the first a-plate 240 and the second a-plate 250 are so-called
A-plate, which satisfies a requirement of
nx≠ny≈nz. In detail, nx is a refractive
index along the slow axis direction, i.e. x direction, of the film plane,
ny is a refractive index along the y direction vertical to the x
direction of the film plane, and nZ is a refractive index vertical
to the film, i.e. z direction, wherein d is a thickness of the film.
Moreover, the first a-plate 240 and a second a-plate 250 provide a first
phase retardation in planar direction and a second phase retardation in
planar direction, respectively. In practice, each of the first phase
retardation in planar direction and the second phase retardation in
planar direction is substantially 140 nm±50 nm. In this embodiment,
each of the first phase retardation in planar direction and the second
phase retardation in planar direction is substantially 140 nm.

[0029] Furthermore, in this embodiment, as shown in FIG. 2A, the first
c-plate 270 is between the LCD panel 210 and the first a-plate 240. The
first c-plate 270 is a uniaxial optical compensation film. For instance,
the first c-plate 270 is a so-called C-plate, which satisfies a
requirement of nx≈ny≠nz, wherein n, is a
refractive index along the slow axis direction, i.e. x direction, of the
film plane, ny is a refractive index along the y direction vertical
to the x direction of the film plane, and nz is a refractive index
vertical to the film, i.e. z direction. The first c-plate provides a
first phase retardation in a vertical direction, wherein the first phase
retardation in vertical direction is substantially 215 nm±100 nm. In
this embodiment, the first phase retardation in vertical direction is
substantially 215 nm, for example. It should be noted that the location
and number of the first c-plate 270 of the present invention may vary
depending on the requirements. Detailed descriptions regarding other
types of the first c-plate 270 varying location and number are set forth
later in the following embodiments, but the present invention is not
limited to these embodiments.

[0030] It is noted that, the biaxial compensation plate 260 has a
plurality of main axes refractive indexes nx, ny and nz,
wherein the definitions of the nx, ny and nz of the
biaxial compensation plate 260 are similar to that of the aforementioned
a-plate and aforementioned c-plate. Specially, nx is a refractive
index along the slow axis direction, i.e. x direction, of the film plane,
ny is a refractive index along the y direction vertical to the x
direction of the film plane, and nz is a refractive index vertical
to the film, i.e. z direction. That is to say, the light propagating in
the biaxial compensation plate 260 performs different velocities in
different propagating directions of the light transmitted in this plate.
Moreover, the main axes refractive indexes nx, ny and nZ
of biaxial compensation plate 260 satisfy the following formula of
Nz=(nx-nz)/(nx-ny), wherein nx>ny, and
-0.5<Nz<1. Nz is defined as a ratio between (nx-nz)
and (nx-ny).

[0031] More specifically, the biaxial compensation plate 260 can be deemed
as a biaxial compensation plate 260 having birefringence characteristics.
The phase retardation Rin in planar direction providing by the
biaxial compensation plate 260 and the phase retardation Rth in
vertical direction are satisfy the formula (1) and the formula (2),
respectively.

Rin=(nx-ny)×d (1)

Rth=(nz-ny)×d (2)

[0032] Designers may adjust the polarizing direction of images by choosing
different phase retardation in vertical direction Rth and phase
retardation in planar direction Rin, such that the optical quality
of the images displayed by LCD 200 may be enhanced, the dark-state light
leakage may be restrained, the viewing angle may be widened, the image
color difference may be compensated, and the problem of the color shift
may be improved. In addition, designers may adjust the polarizing
direction of light by choosing different nx-nz and
nx-ny satisfying the relationship of -0.5<Nz<1, so as to
increase luminous flux of the light passing through LCD panel 210.

[0033] In this present embodiment, the biaxial compensation plate 260 is
disposed between the first polarizer 220 and the first a-plate 240.
Certainly, the biaxial compensation plate 260 may also be disposed
between the second polarizer 230 and the second a-plate 250, a location P
pointed to by an arrow shown as FIG. 2A, but the present invention should
not be limited to this.

[0034] In practice, when the main axes refractive indexes of the biaxial
compensation plate 260 satisfy the relationship of -0.5<Nz<1,
the phase retardation of the vertical alignment LCD 200 can be
efficiently compensated by the certain optical parameters of the biaxial
compensation plate 260. Hence, the dark-state light leakage can be
efficiently restrained, thus widening the viewable angle of the LCD 200.

[0035] FIG. 2B is a schematic view showing the viewing angle-contrast of
the LCD depicted in FIG. 2A. Referring to FIG. 2B, in this embodiment,
the first phase retardation in planar direction and the second phase
retardation in planar direction are substantially 140 nm respectively,
the first phase retardation in vertical direction is substantially 215
nm, and the phase retardation of vertical alignment liquid crystal layer
216 is substantially 340 nm. The optical parameters of the biaxial
compensation plate 260 are designed to cooperate with phase retardations
of the foregoing elements. In this present embodiment, the Nz value of
the biaxial compensation plate 260 is substantially 0.275, and the phase
retardation of the biaxial compensation plate 260 is substantially 170
nm. As shown in FIG. 2B, compared to the viewing angle--contrast of the
conventional LCD 100 shown as FIG. 1B, the LCD 200 of the present
embodiment not only can efficiently improve the viewing angle of top
direction, bottom direction, left and right directions, but also can
improve the viewing angle of diagonal direction.

Second Embodiment

[0036] FIG. 3A illustrates a schematic view of a liquid crystal display
according to the second embodiment of the present invention. Referring to
FIG. 3A, the LCD 300 is similar to the LCD 200 of the first embodiment, a
single c-plate is likewise disposed in the LCD 300. Furthermore, in this
embodiment, the first c-plate 270 is individually disposed between the
LCD panel 210 and the second a-plate 250. Similarly, the biaxial
compensation plate 260 is capable of suppressing the dark-state light
leakage phenomenon of the LCD 300, and further widening the viewing angle
and improving the optical quality.

[0037] FIG. 3B is a schematic view showing the viewing angle-contrast of
the LCD depicted in FIG. 3A. Referring to FIG. 3B, in this embodiment,
the Nz value of the biaxial compensation plate 260 is substantially
0.275, and each of phase retardation of each of the first a-plate 240,
the second a-plate 250, the biaxial compensation plate 260 and the first
c-plate 270 is similar to the first embodiment. As shown in FIG. 3B,
compared to the conventional LCD, the LCD 300 of the present embodiment
not only can efficiently improve the viewing angle of top direction,
bottom direction, left and right directions, but also can improve the
viewing angle of diagonal direction.

The Third Embodiment

[0038] FIG. 4A and FIG. 4B illustrate a schematic view of a liquid crystal
display respectively according to the third embodiment of the present
invention. Referring to FIGS. 4A and 4B, the LCD 400 and 500 are similar
to the LCD 200 of the first embodiment. Furthermore, the LCD 400 and 500
of this embodiment further comprise a second c-plate 280, and the first
c-plate 270 and the second c-plate 280 are adjacent to two sides of LCD
panel 210 respectively. That is to say, two c-plates 270 and 280 are
simultaneously utilized in this embodiment. In detail, the second c-plate
280 is disposed between the LCD panel 210 and the second a-plate 250. The
difference between the LCDs shown in FIG. 4A and FIG. 4B is the location
of the biaxial compensation plates 260, wherein the biaxial compensation
plates 260 of LCD 400 shown in FIG. 4A is disposed between the first
polarizer 220 and the first a-plate 240, and the biaxial compensation
plates 260 of LCD 500 shown in FIG. 4B is disposed between the second
polarizer 230 and the second a-plate 250.

[0039] It should be noted that, in this embodiment, a summation of phase
retardations provided by the first c-plate 270 and the second c-plate 280
is substantially equal to a phase retardation in vertical direction
provided by the first c-plate 270 of the first embodiment or provided by
individually utilizing the first c-plate 270. In other words, the
summation of phase retardations provided by the first c-plate 270 and the
second c-plate 280 is substantially equal to a phase retardation in
vertical direction provided by the first c-plate 270 excluded from the
second c-plate 280, specifically, the phase retardation in vertical
direction provided by the first c-plate 270 of the first embodiment is
215 nm, for instance. In this embodiment, the phase retardation in
vertical direction provided by the first c-plate 270 is 107.5 nm, for
example, and the phase retardation in vertical direction provided by the
second c-plate 280 is 107.5 nm, for example.

[0040] In this embodiment, the first phase retardation in planar direction
and the second phase retardation in planar direction are substantially
140 nm respectively. The first retardation in vertical direction is
substantially 107.5 nm, and the second retardation in vertical direction
is substantially 107.5 nm. The phase retardation of the vertical
alignment liquid crystal 216 is substantially 340 nm. The optical
parameters of the biaxial compensation plate 260 are designed to
cooperate with the foregoing elements, in this embodiment, the Nz value
of the biaxial compensation plate 260 is substantially 0.275, and the
phase retardation of the biaxial compensation plate 260 is substantially
170 nm.

[0041] FIG. 5A and FIG. 5B illustrate a schematic view showing the viewing
angle-contrast of the LCD respectively depicted in FIG. 4A and FIG. 4B.
As shown in FIG. 5A, compared to the conventional LCD, the LCD 400 and
500 of the present embodiment not only can efficiently improve the
viewing angle of top direction, bottom direction, left and right
directions, but also can improve the viewing angle of diagonal direction.

[0042] In view of the above, the LCD of the present invention expects
widening the viewing angle entirely, it can also provide a remarkable
improvement for the color difference phenomenon with a large viewing
angle. FIG. 6A and FIG. 6B illustrates a schematic view showing actual
measuring chromaticity coordinates in different viewing angles of a
conventional LCD and one embodiment of the present invention LCD
respectively. As shown in FIG. 6A and FIG. 6B, when viewing the LCD of
the present embodiment in different viewing angles, the distribution of
the observed red color performance R, the observed green color
performance G, and the observed blue color performance B on the
chromaticity diagram are more concentrated. Accordingly, the LCD of the
present invention can improve when users view the LCD with a large
viewing angle.

[0043] According to the above descriptions, this invention enhances the
optical effect by utilizing a biaxial compensation plate satisfying a
certain condition and properly adjusting the polarizing direction of
images displayed by the LCD panel. Moreover, compared to the conventional
LCD, the LCD of the present invention can efficiently suppress the
dark-state light leakage, widen the viewing angle, improving the color
difference with large viewing angle, and improve the display quality of
the LCD.

[0044] Although the present invention has been disclosed by the above
embodiments, they are not intended to limit the present invention. Any
person having ordinary knowledge in the art may make some modifications
and alterations without departing from the spirit and scope of the
present invention. Therefore, the scope for which protection is sought by
the present invention falls in the appended claims.

Patent applications by Chun-Chi Chi, Taichung County TW

Patent applications by Yi-Chun Wu, Hualien County TW

Patent applications by Yu-Chen Liu, Taipei City TW

Patent applications by WINTEK CORPORATION

Patent applications in class Compensator or retarder (i.e., not using liquid crystal cell)

Patent applications in all subclasses Compensator or retarder (i.e., not using liquid crystal cell)